let canvas, ctx, w, h, hue, stars, count, maxStars;
let canvas2, ctx2;
let half, gradient2;

function init(elCanvas) {
  canvas = elCanvas;
  ctx = canvas.getContext('2d');
  w = canvas.width = window.innerWidth;
  h = canvas.height = window.innerHeight;
  hue = 217;
  stars = [];
  count = 0;
  maxStars = 1200;

  canvas2 = document.createElement('canvas');
  ctx2 = canvas2.getContext('2d');
  canvas2.width = 100;
  canvas2.height = 100;
  half = canvas2.width / 2;
  gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);
  gradient2.addColorStop(0.025, '#fff');
  gradient2.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)');
  gradient2.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)');
  gradient2.addColorStop(1, 'transparent');

  ctx2.fillStyle = gradient2;
  ctx2.beginPath();
  ctx2.arc(half, half, half, 0, Math.PI * 2);
  ctx2.fill();

  for (let i = 0; i < maxStars; i++) {
    new Star();
  }
}
// End cache

function random(min, max) {
  if (arguments.length < 2) {
    max = min;
    min = 0;
  }

  if (min > max) {
    let hold = max;
    max = min;
    min = hold;
  }

  return Math.floor(Math.random() * (max - min + 1)) + min;
}

function maxOrbit(x, y) {
  let max = Math.max(x, y),
    diameter = Math.round(Math.sqrt(max * max + max * max));
  return diameter / 2;
}

let Star = function () {
  this.orbitRadius = random(maxOrbit(w, h));
  this.radius = random(60, this.orbitRadius) / 12;
  this.orbitX = w / 2;
  this.orbitY = h / 2;
  this.timePassed = random(0, maxStars);
  this.speed = random(this.orbitRadius) / 900000;
  this.alpha = random(2, 10) / 10;

  count++;
  stars[count] = this;
};

Star.prototype.draw = function () {
  let x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
    y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY,
    twinkle = random(10);

  if (twinkle === 1 && this.alpha > 0) {
    this.alpha -= 0.05;
  } else if (twinkle === 2 && this.alpha < 1) {
    this.alpha += 0.05;
  }

  ctx.globalAlpha = this.alpha;
  ctx.drawImage(
    canvas2,
    x - this.radius / 2,
    y - this.radius / 2,
    this.radius,
    this.radius
  );
  this.timePassed += this.speed;
};

function animation() {
  ctx.globalCompositeOperation = 'source-over';
  ctx.globalAlpha = 0.8;
  ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 1)';
  ctx.fillRect(0, 0, w, h);
  ctx.globalCompositeOperation = 'lighter';
  for (let i = 1, l = stars.length; i < l; i++) {
    stars[i].draw();
  }

  window.requestAnimationFrame(animation);
}

let huhuiyu = {
  startAnimate(el) {
    el.innerHTML = '';
    let elCanvas = document.createElement('canvas');
    el.appendChild(elCanvas);
    huhuiyu.el = elCanvas;
    init(elCanvas);
    animation();
  },
};

export default huhuiyu;
